For a general connected undirected graph \(\mathcal {G}\)  (which can be interpreted as a strongly connected directed graph where each edge has the complement edge with different direction), the matrix \(L = DD^T \in \mathbb {R}^{c\times c}\)  is called the Laplacian matrix, and it is also known as graph Laplacian, admittance matrix or Kirchoff matrix in various different applications. The Laplacian matrix \(L\)  has been used to represent the graph of electrical circuits and power networks [1]}, [2]}, as well as, of balanced CRN with mass-action kinetics [3]}.
It satisfies
\(0=\lambda _1(L)<\lambda _2(L)\le ...\le \lambda _n(L).\) 
